Process of recovering solvents.



T. BAKER.

PROCESS 0F RECOVERING SOL'VENTS.

APPLICATION FILED MAR. 26. i915.

1,218,616. y Patented 1131111917.

` 2 SHEETS-SHEET I. ZW] 3 T. BAKER.

PROCESS 0F RECOVERING SOLVENTS. APPLICATION FILED MAR. 26, 1915.

1,218,616.' Patented Mar. 13, 1917.

2 SHEETS-SHEET 2.

l OO OO 'NAf-)000000000 Lfoqynooooooo A TTOH/VEYS THEODORE BAKER, OFWILMINGTON, DELAWARE, ASSIGNOR TO E. I. DU PONT D.; NEMOURS POWDERCOMPANY, OF WILMINGTON, DELAARE,` A. CORPORATION OF NEW JERSEY.

PROCESS OERECOVERING SOLVENTS.

Patented Mar. 13, 1917.

Original application led October 7, 1912, Serial No. 724,309. Dividedand this application filed March 26,

1915. Serial No. 17,167. Y

To all whom t may concern:

Be it known that I, THEoDoRE BAKER, of

Wilmington, in the county of New Castle,

and in the State of Delaware, have invented a certain new and usefulImprovement in Processes for Recovering Solvents, and do hereby declarethat the following is a full, clear, and exact description thereof.

My invention relates particularly to a method for recovering solventsused in coating compositions, although it may be adapted to use in anyother connection where it is desired to recover solvents. My inventionis particularly applicable to the recovery of solvents from coatings ofpaper or teXtile fabrics containing india-rubber, pyroXylin, oils,paints or varnishes, and employing volatile solvents such as benzol,alcohol, ether, acetone or turpentine.

The object of my inventionn is to render the recovery of solvents morecomplete than has hitherto been possible, to render the danger ofexplosion as slight as possible, and to improve the quality of theproduct as well as the convenience and economy of operating theapparatus used for recovering the solvent.

My invention is carried out by passing the goods in a continuous coatedweb through an evaporating chamber where it issubmitted to the action ofaheated current of air. The air in the evaporating chamber having takenup the solvent evaporated is conducted to a condenser, where a. portionof the solvent is condensed, the air with thev residual solvent beingagain heated and returned to the eva-p orating chamber, while thecondensed solvent, after purification, isemployed in pre-' paring freshcoating compositions. In car-Y rying out my invention advantage is takenof the difference in densities ofthe vapors in the interior ofthe'apparatus to effect the circulation thereof. The 'vapors within theinterior of the evaporating chamber have ldifferent densities owing tordifferent temperatures and the different quantities of solvent vaporcarried by the circulating air. It' is advantageous to provide acirculation which is effected without the use of special forcing meansfor the reason that great differences in' local pressures are therebyavoided and there is not the great consequent tendency for leakage.Furthermore, in the type of circulation which I use, there is nomechanical apparatus to break down. and thereby stop the circulationduring the operation of the apparatus..

While my process is capable of beingcarried out in manydiferent types ofapparatus, I have shown only certain modifications of apparatus which lImayfuse, in the accompanying drawings, in which- Figure l is a verticaltransverse section of one form of apparatus in which my process may becarried out, the parts being shown somewhat diagrammatically; v

Fig. 2 is a similar view of another type of apparatus which I may use;

Fig. 3 is a similar view of still another type of apparatus;

Fig. 4 is a similar view-of anothertype of apparatus used for the same,purpose; and

Fig. 5 is also a similar view of another type of apparatus used for thesame purose. y

In `the drawings, reference being had rto Fig. l, a traveling web l ofpaper or textile fabric, after being coated, is conveyed through anevaporating chamber .2 by `.any suitable means While in the evaporatingchamber 2, the web 1 passes beneath a series of heating coils 3 forevaporating `the volatile liquids from the coating composition. Theevaporating chamber is covered by 'an easily-removable cover 4, theedges of which are rendered air-tight by being retained in a liquid seal5, filled with castor oil or other liquid, or in any other convenientmanner as by i fastening with adhesive tape.- The current of air whichis circulating through,

said chamber is led therefromdownwardly through a vertical passagegcontaining, at the upper end thereof, a series of cooling coils 7 toincrease the' specific gravity of the solvent-laden air, and to cool thesame preliminary to the condensationand separa-.-

tion of the solvent therefrom. The cooled current of air carrying thesolvent vaporsis then conducted through ahorizontallydisposed condenser8 over a series of` cooling coils 9. The series of coils 9 1s fed with acurrent of cold water or other refrigeratlng agent through an inlet 10and discharges the i same'through an outlet A11. the bottom of thecondenser 8 there is a dlscharge pipe 12 for the condensed solvent. Theair hav.

ing had part of its contained solvent removed by condensation isreheated in any convenient manner as by passing over steam coils 14. Thedensity being thereby reduced, it rises through a vertical passageway 13and then returns to the evaporating chamber for re-use. as before. Abalile 15 is provided to keep scrapings of coating material from fallingdown the flue 13 and to better direct the circulation of the air.

The type of apparatus shown in Fig. 2 1s constructed 'in vthe samemanner as that shown in Fig. 1, except that an elevated side chimney isemployed to assist the draft, 15 thus enabling the otherl parts to bebuilt more compactly without sacrificing the eiliciency of circulation,attained in the form shown in Fig. 1. In the form 'shown in Fig. 2, thisdifference in construction requires the solvent-laden air to be leddownwardly past a lbaiiie plate 16 to an upwardly directed chamber 17over a baille plate 18, and downwardly through the vertical passageway6, over the cooling coils 7. The long passageway 6 materially assists ingiving the circulating current'of air the required speed.

The form of apparatus shown in Fig. 3 is the same as that shown in Fig.1, except as follows After leaving the""evaporating chamber 2, thesolvent-laden air is conducted directly into a` horizontal. flue 19located immediately below the evaporating chamber and from this pointitis led di. rectly to the vertically disposed condenser 20 having a setof cooling coils 21. The air which has been freed from the surplussolvent is thereafter led into contact with the reheating coils 14located in the vertical passageway 13. This arrangement avoids the lossof any space in the middle of the apparatus between the severalchambers.

Another and more compact form of apparatus is shown inl Fig. 4 in whichthe construction is the same as in the case ofthe v modification shownin Fig. 1, except that the condenser 8 is located immediately below tthe evaporating chamber 2, the vertical passageways 6 and 13 being mademuch wider to compensate for their shortness, and bae plates 22 and 23being located at the inlet and outlet ends of the condenser at the topthereof, and a baliie plate 24 being located at the bottom of thecondenser at the outlet thereof to keep .the condensed solvent y awayfrom the reheating arrangement.

In Fig. 5 I have shown a type of apparatus which is the same as-thatshown in Fig.

4, except that a passageway 17 and a1 passageway 6, together with bailleplates 16 and 18 are utilized which are similar to those shown in theform in Fig. 2. This type of apparatus gives a somewhat bettercirculation than that shown in Fig. 4, owing to the added length of thepassageway 6.

The forms show'n in Figs. 4 and5 have j the advantage that the condensedsolvent is delivered at a high level, and that the space below theapparatus is entirely unencumbered.

The operation of my process is substantially the same in all of thedifferent forms of apparatus, and is as follows: The coated web beingconstantly moved through the apparatus, the body of air containedtherein is first heated by the reheating coils, thereby decreasing itsdensity, and increasing its evaporating capacity. The ,heated current of`air is then conducted over the coatedsurface which is at the same timesubjected to theheat radiated from the heating coils located above thesame. The heat lost by the coated web and the air in contact with it,due to the latent heat of evaporation is made good by radiation from thecoil above in the upper part 4of the evaporating chamber, thus enablingva smaller volume of circulated air to effect the same amount ofevaporation and a higher concentration of evaporated solvent to bereached, as Well as more uniform Vand rapid drying, without risk ofoverheating. The current of air carrying a large percentage ofevaporated solvent, is now cooled to the saturation point by contactwith the cooling coils 7 The mixed air and solvent vapors thereuponacquire theirv greatest density, and fall at considerable speeddownwardly through the vertical passageway 6 until the condenser isreached. The available part of the solvent is then condensed upon thesurfaceof the cooling coils in the condenser, and' is separated outandremoved through the discharge pipe Y12 located at the bottom thereof. Aportion of the solvent having now been separated from the current ofair,

the latter is again conducted upwardly into contact with the heatingcoils 14, thereby decreasing the specic gravity of the same and causingit to agaln circulate in contact with the coating to be dried.

This application is a division of my application for processandapparatus for recovering solvent, Serial No. 724,309, filed October 7,1912.

WhileI have shown and described abovei only certain forms of the processand ap paratus which may be used for the carrying out of my invention, Iwish it to be understood that many changes may be made therein withoutdeparting from the fundamental principles thereof.

1. rIhe process which comprises eiiecting v the evaporation. of volatilesolvent from a coating c ontalnlng the same by a gaseous l currentclrculated by convection, said gase` ous current falling directly fromthe coatlng. v

2. The process which comprises effecting.

the evaporation of volatile solvent from aA 7 coating containing thcsame by a gaseous current circulated by convection, induced bycondensing the volatile solvent from the gaseous current, which fallsdirectly from the coating.

3. The process which comprises effecting the evaporation of volatilesolvent from a coating containing the same by a gaseous currentcirculated by convection, induced by lowering the temperature of acurrent thereof descending directly from the coatlng. v

4. The process which comprises effecting the evaporation of volatilesolvent from a coating containing the same by a gaseous currentcirculated by convection, induced by condensing the volatile solventfrom the coating.

In testimony that I claim the foregoing I have hereunto set my hand.

THEEODORE BAKER'.

Witnesses I. E. STRIACKLAND, R. H. RAWLEIGH.

